Introduction to Cells: Cell Structure, Function, and Clinical Relevance

Flashcards testing core concepts, organelle structures and functions, membrane transport mechanisms, cell theory, and clinical correlations from the Introduction to Cells lecture.

What structural hierarchy of biological organization is illustrated in this diagram, starting from the cell level up to the complete human body?

Cell (Cardiomyocyte) $\rightarrow$ Tissue (Cardiac muscle tissue) $\rightarrow$ Organ (Heart) $\rightarrow$ Organ system (Cardiovascular system) $\rightarrow$ Organism (Human body).

What are the three core principles of the cell theory?

1. All living organisms are composed of one or more cells.
2. The cell is the basic structural and functional unit of life.
3. All cells arise from pre-existing cells.

How do prokaryotic and eukaryotic cells compare regarding typical size and chromosome structure?

Prokaryotic cells are generally smaller ($\approx 0.1–5\,\mu\text{m}$) with a single circular DNA chromosome in the nucleoid. Eukaryotic cells are generally larger ($\approx 10–100\,\mu\text{m}$) with multiple linear chromosomes associated with histones inside a true nucleus.

Which human diseases caused by bacterial pathogens are listed as examples in the lecture, and what prokaryotic structures do targeted antibiotics exploit?

Tuberculosis and cholera; targeted antibiotics exploit bacterial structures and processes including bacterial ribosomes (70S) and cell-wall synthesis (peptidoglycan in bacteria).

Why is cellular compartmentalization important in eukaryotic cells?

It creates distinct microenvironments, increases the efficiency and regulation of cellular processes, allows simultaneous functions that would otherwise be incompatible in the same space, and enables specialized functions in multicellular organisms.

Which cellular organelles are classified as double-membrane organelles, and which are non-membranous?

Double-membrane organelles: Nucleus and Mitochondria. Non-membranous structures: Ribosomes, Cytoskeleton (microfilaments, intermediate filaments, microtubules), and Centrosome (with centrioles).

What is the approximate percentage composition of the four main components of the plasma membrane?

Phospholipids ($\sim 50\%$), Proteins ($\sim 30\%$), Cholesterol ($\sim 20\%$), and Carbohydrates ($5-10\%$).

What is the primary distinction between passive transport and active transport across the plasma membrane?

Passive transport requires no ATP and moves substances down their concentration gradient (high $\rightarrow$ low). Active transport requires energy (ATP or an ion gradient) and moves substances against their concentration gradient (low $\rightarrow$ high).

How do primary active transport and secondary active transport differ in their energy sources?

Primary active transport directly uses energy from ATP hydrolysis (e.g., $Na^+/K^+$ ATPase). Secondary active transport uses energy stored in an ion gradient, usually $Na^+$ (e.g., $Na^+$/glucose symporter SGLT).

Which clinical conditions are associated with mutations in the LDL receptor and CFTR channel, respectively?

LDL receptor mutation causes familial hypercholesterolemia, while CFTR channel mutation causes cystic fibrosis.

What is the structural distinction between the cytoplasm and the cytosol?

Cytoplasm is the portion of the cell inside the plasma membrane but outside the nucleus (consisting of cytosol, organelles, and inclusions). Cytosol is specifically the aqueous, gel-like fluid component of the cytoplasm.

What are cellular inclusions, and what are three examples?

Inclusions are non-membrane-bound accumulations of stored materials. Examples include glycogen granules, lipid droplets, and pigments.

What are the primary functions of the nucleolus within the nucleus?

It synthesizes ribosomal RNA (rRNA, mainly 18S, 5.8S, and 28S rRNA) and assembles ribosomal subunits with ribosomal proteins imported from the cytoplasm.

Which signal sequences and transport proteins mediate nuclear import and export through nuclear pore complexes?

Nuclear import: Nuclear localization signals (NLS) recognized by importins. Nuclear export: Nuclear export signals (NES) recognized by exportins.

What genetic defect causes Hutchinson-Gilford Progeria Syndrome, and what is its cellular effect?

Pathogenic variants in the LMNA gene affect lamin A (a key component of the nuclear lamina), causing abnormal nuclear shape, impaired nuclear organization, premature aging, growth failure, and early cardiovascular disease.

Compare the sedimentation coefficients and subunits of eukaryotic cytosolic ribosomes and bacterial ribosomes.

Eukaryotic cytosolic ribosomes are 80S (composed of 60S large and 40S small subunits). Bacterial ribosomes are 70S (composed of 50S large and 30S small subunits).

What distinguishes the destination of proteins synthesized by free ribosomes versus ER-bound ribosomes?

Free ribosomes synthesize proteins that function in the cytosol or are targeted to the nucleus, mitochondria, peroxisomes, or other organelles. ER-bound ribosomes synthesize proteins that enter the endomembrane system (secreted proteins, integral membrane proteins, and lysosomal enzymes).

Which specific antibiotic classes target the 30S ribosomal subunit versus the 50S ribosomal subunit in bacteria?

Tetracyclines and aminoglycosides bind to the 30S subunit; macrolides bind to the 50S subunit.

What is Diamond-Blackfan anemia, and what is its primary clinical feature?

It is a ribosomopathy caused by pathogenic variants in genes encoding ribosomal proteins that impair ribosome biogenesis; it typically presents with macrocytic anemia in infancy due to reduced protein synthesis in bone marrow erythroid progenitor cells.

Contrast the primary functions of the rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).

Rough ER is predominantly involved in protein synthesis, co-translational translocation, protein folding (assisted by chaperones like BiP), initial post-translational modification (N-linked glycosylation), and packaging into COPII vesicles. Smooth ER is involved in lipid and steroid synthesis, carbohydrate metabolism (glucose-6-phosphatase), drug/xenobiotic detoxification (cytochrome P450), and $Ca^{2+}$ storage/release.

Describe the molecular defect and clinical consequence of alpha-1-antitrypsin deficiency.

Mutations in the SERPINA1 gene cause misfolding of $\alpha_1$-antitrypsin and its accumulation in the rough ER of liver cells, leading to ER stress, hepatocyte injury, liver disease (e.g., cirrhosis), and early-onset emphysema due to low circulating $\alpha_1$-antitrypsin.

What are the three main regions of the Golgi apparatus stack in order of anterograde cargo flow?

cis-Golgi network (CGN, receiving side) $\rightarrow$ Medial cisternae $\rightarrow$ trans-Golgi network (TGN, sorting and dispatch side).

What biochemical defect causes I-cell disease (Mucolipidosis II), and what is the cellular consequence?

Failure to add mannose-6-phosphate (M6P) tags to lysosomal enzymes in the Golgi apparatus, causing lysosomal enzymes to be secreted outside the cell instead of targeted to lysosomes, leading to accumulation of undegraded material in lysosomes.

How does pH change along the endocytic pathway from early endosomes to lysosomes, and what pump drives this acidification?

Early endosomes (pH $\sim 6.0-6.5$) $\rightarrow$ Late endosomes (pH $\sim 5.0-5.5$) $\rightarrow$ Lysosomes (pH $\sim 4.5$). Acidification is driven by V-ATPase proton pumps.

How do mutations in the LDLR gene disrupt endosomal trafficking in Familial Hypercholesterolemia?

Mutations lead to a reduced number or defective function of LDL receptors, impairing receptor recycling and decreasing cellular uptake of LDL, which causes elevated plasma LDL-cholesterol and increased risk of premature atherosclerosis.

What three main pathways deliver cargo to lysosomes for degradation?

1. Endocytosis (heterophagy)
2. Phagocytosis (heterophagy)
3. Autophagy (degradation of intracellular components)

What is the underlying cause of Lysosomal Storage Disorders (LSDs), and what is an example disease and affected enzyme?

An inherited deficiency of a lysosomal hydrolase leading to the accumulation of undegraded substrates inside lysosomes. An example is Gaucher disease, caused by a deficiency of $\beta$-glucocerebrosidase.